Process of selectively refining petroleum oils



Patented F eb. 10, 1942 Incense OF QSELECTIVELY REFINING {PETROLEUM OILSv Arthur W. H-ixson, Lenma, .N. J., and Ralph Miller,:New 1ork, N. Y.,assignors to The Chemical Foundation, Incorporated, a corporation ofDelaware N Drawing. Original application December 17, l'93'6fserialN0.'116,348. 'Divided-and this' application-April 23, 1940, Serial'N 0.331,158

LThisinven tion relates to the frajc'tionation of oils, :more.particularly to the separation of petroleum .oil 'into a series-ofdesirable, valuable fractions :by -a sp'ecial system of fractionalextraction. V V

Petroleumoil, as is known, comprises essentially acomplexmix-ture: ofdifferent homologous series or groups of hydrocarbons-such asparatfinic', naphthenic, and aromatic constituents. When petroleum oilis separated into thecom- 'mercially useful fractions, such-for exampleas the gas foil, lubricating-oil; and'iul oil fractions, the *samegeneral complexity still obtains, although "the respective percentagesof the different groups in such commercialfractions may vary. Thus atypical, relatively high boiling range distillate, having thecharacteristics of' lubricating toil, contains' p'araifinc, naphthenicand aromatic constituents and some -"asphalt. "The respectiveproportions of 1 such i constituents Y I dependupo'n the type orsource'of the crud oil. Thus Pennsylvania oil contains little or noasphalt "and a relatively small amount of aromatics. :IfheCoastal(oilgconversely, has a relatively high percentage of asphalt andaromatics.

l\/l-id-Continent"oiltis approximately an interme-.

possesses the *best lubricating properties and itaefi iisrfonthisreasonthatl'the Pennsylvania base oil constitutes the accepted standard.

It is also well recognized that T the parafiinicity .of agivenlubricating .oillfrac'tion may be in- :creased' by treating Jsuchffractio'n to remove;

Such processes consist essentially;

the paraffinic constituents of the starting mate- 515 lrial. The two'fra'ctions "are then *subj'ected'to distillation to remove thecontained solvent. Modifications of such extraction processes includethe use of dual solvents,'theiretreatment"or the raffinate with theoriginal solvent or ,a spe- -cifically different solvent to further-refine it, and the like. The desideratum in all such prior -methods,however, has been to enhance the selectivity of the fractionation "forthepurpose or securing the maximum yield of the high viscosity indexparafiinic fraction.

To render such processes commercially feasible it is necessary-toseparate and recover the solvent which is employed. This is usuallydone, as noted, by vacuum distillation. 'The residual 'naphthenic oil orextract is thus more naphthenic than the original oil whichwas-subjected to the treatment. "This extract howeve'r, because of therelatively large p'ercentage or contained asphalt, is a viscous, tacky,black, tar-like product. The quantity of the asphalt in 'a given extractwill, of courseyvary dependin'g -u pon the type of lubricating 'oilstock treated. It is greatest-in the extract iproduced from theasphaltic base oils. Such extract, although relativelylfree fromparafi'mic constituents, does contain an appreciable quariti'ty ofpotentially valuable oil. However, due :td' the large percentage ofasphalt contained in the "extract, such'ira'ction is practically usefulonly as a cracking tstock .since it is too difiicult "and expensive toseparate the oil from a fraction .of "a 'high asphaltconcentration.

If the oil which to :be treated is not ideasphalted and ,contains'anappreciable amount of asphalt, solvent refining will I not remove theas- 'phalt'from the paraffin fractions, although such asphalt 'will beconcentrated, to a considerable degree, in the extract layer. It is ofcourse :possible to "remove the asphalt from the 'oil prior to solventextraction. If the oil is deasphaltedto'a certain extent, selectivesolvents will then dissolve the "residual'asphalt, the "color :bodies,the aromatic and 'naphthenic "constituents, but will not ad-issolv'e theiparaflinic hydrocarbons.

The" typical process of solvent extraction'is, in effect, amethod ofseparating various constituents present in the oil. If, 'as is usuallythe case, the extraction process is foperated 'to produce a'raffinate':of "high viscosity index from an initial v:or startingmaterialhaving but a small percentage of 'high viscosity index oil, itis clear that the-yield of theparaflinic fraction must necessarily below. In thes circumstances, be- -cause of the characteristics :of theextract, 'the .properties. tion would constitute a marketablelubricating remainder of the oil is employable only for crackingpurposes.

The present invention, as will more fully appear, is based on theconcept of recovering the maximum values from a given petroleum stock bynot only extracting a valuable high viscosity index raflinate, but alsoby effectively utilizing the phenomenon of preferential solubility forthe recovery of a more valuable secondary fraction than has beenpossible heretofore.

If the oil constituents of the extract could effectively andeconomically be separated from the associated asphalt, then a number ofmajor advantages would obtain. Thus, from a given starting material,such for example as a Mid- Continent lubricating oil fraction, therecould be obtained two substantially asphalt-free lubricating oilfractions and a residuum of a high asphalt concentration. The firstlubricating oil fraction would comprise a valuable, high viscosity indexrafiinate of excellent lubricating The second novel, recoverable fracoilfraction of lower viscosity index, comprised largely of naphthenic andaromatic hydrocarbons substantially free from asphalt. Finally,

the third fraction would comprise an oil of a high asphalt concentrationwhich, being less refractory than the extract, constitutes a good lowtemperature cracking stock. Again this third fraction may suitably betreated, by methods known to those skilled in the art, to producevaluable products, such as road oils, binders, mastics, and the like.

It has been found that such advantages may be attained and theenumerated novel results secured by a method which is not only simpleand effective but which also may readily be correlated with presentmethods of solvent extraction.

A major object of the present invention is to devise a method ofproducing commercially valuable fractions from petroleum oils.

Another object is to provide a method of separating and recovering themore valuable constituents of the naphthenic-like extracts from the lessvaluable constituents.

Yet another object is to product a novel type of petroleum crackingstock.

An additional object is to devise an eiiective method of selectivelyextracting parafiinic and naphthenic fractions from anasphalt-containing oil.

With these and other equally important and related objects in view, theinvention comprehends the concept of subjecting a natural orpyrogenetically produced petroleum oil fraction to a special type ofsequential, selective solvent extraction to recover therefrom a fractionof higher paraifinicity than the original oil, a second oil fraction ofhigher naphthenicity than the original oil, and a residual fraction inwhich the asphalt of the starting material is largely concentrated. Insharp contradistinction to prior art methods, in which the original oilwas separated into a raflinate and a cracking stock of low value, thepresent method insures the recovery of a number of valuable fractions.Thus operating under the present method there is produced an excellentlubricating fraction of optimum parafiinicity, a valuable naphtheniclubricant substantially free from tarry matter, and a viscous residualoil of high asphalt concentration.

sion of the discovery explained in application Serial No. 60,634, onwhich Patent No. 2,143,145 was granted January 10, 1939, and to thisdegree the present application is a continuation in part of the priorapplication. As explained in that application, a certain class ofsolvents possesses a striking preferential solvent action on thenon-parafi'inic constituents of a mixed oil The present invention is, ina sense, an extenbase. It was further explained that the highselectivity of these solvents is due to the unequal distribution of theelectronic charges of the molecule, i. e. its polar characteristics, andthat the effective index of selectivity of a solvent is its dipolemoment. It was additionally pointed out that solvents which werecharacterized by a high dipole moment and which also possessed the otherdesirable characteristics, such as low melting point, miscibility atelevated temperatures, immiscibility at lower temperatures, etc., servedmost effectively as single solvents for the separation and recovery ofraffinate.

It is now found that this characteristic of optimum selectivity ofcertain solvents for the non-paraflinic constituents renders thempeculiarly useful for the production of substantially asphalt-freenaphthenic-like oil fractions. This result can be achieved by treating asolution of the non-paraflinic constituents in a highly selectivesolvent with a second solvent which functions to extract a certainpercentage of the lighter oil from the selective solvent, leaving in theselective solvent phase the heavier asphalt constituents.

In the preferred embodiment of the present invention the first solventis preferably one which is characterized by a high selectivity andrelatively low solubility, such for example as ortho-nitroanisole andortho-methoxybenzonitrile. As will appear more fully hereinafter,however, the present invention is not limited to these particularsolvents but is available for employment with any solvent whichpossesses a marked selectivity for the naphthenic fractions and which isimmiscible with the clarifying solvent.

In order to insure the improved results mentioned it will be appreciatedthat the second or clarifying solvent must possess certaincharacteristics. It must be a solvent for oil although, as will beunderstood, it need not be selective with respect to paraflinic andnaphthenic oils.

It must of course be immiscible with the selective naphthenic solvent atthe temperature at which stratification is to be effected, andpreferably should be immiscible with the selective solvent even atrelatively elevated temperatures. It must be amenable to use with theparticular selective naphthenic solvent employed. The clarifying solventshould also be of such a character as to be employable without the useof expensive equipment.

A typical illustrative solvent of this type which eifectively fulfillsthe enumerated prerequisites is tri-amylamine. This alkyl amine isinsoluble in water; it has a marked solubility for oil at anytemperature; it has a distillation range of 230 C. to 260 C., and aspecific gravity of .7937 at 20 C. It dissolves ortho-nitroanisole, oneof the preferred solvents, only very slightly at room temperature and iscompletely miscible with ortho-nitroanisole at C. This, as will beappreciated, is a wide permissive operating range. Since the clarifyingsolvent may be contacted with the selective solvent-naphthenic oil phaseagerzaam at any temperature below this miscibility temperature, thesolubility of the tri-amy'laminefor the oil bodies can be modified to aconsiderable degree to thus controlthe amount and/or quality of the oilremoved from the selective solvent phase.

As will be seen more fully hereinafter, the major desirablecharacteristics of the selective solvent are maximum selectivity andrelatively low solubility. The salient characteristics upon which thechoice of the clarifying solvent is based are, as noted, a markedsolubility for oil bodies at any temperature, relatively low selectivityand a high temperature of miscibility with the selective solvent.

Tri-amylamine is peculiarly effective for the purposes of the presentinvention and serves Well to illustrate the principles involved, as isshown by the following treatment.

A given quantity of a mixed base oil was treated with 246% by weight ofortho-nitroanisole in a continuous, countercurrent extraction system.The mass was heated to the miscibility temperature, as explained in theapplication referred to, Serial No. 60,634, and the temperature at thesolvent outlet of the system was'held at approximately C. Under thesecircumstances, upon analysis it was found that 29% of the original oilwas removed in the solvent phase, the remainder constituting a highviscosity index raffinate. The solvent phase was then treated withtri-arnylamine in the same countercurrent system in which thetemperature of the mass was maintained at substantially 26 C. The amountof tri-amylamine used was 83% by'weight of the original oil. Thetri-amylamine fraction was segregated from the ortho-nitroanisolefraction and was subjected to vacuum distillation. It was found that asmall amount of ortho-nitroanisole was recovered in the distillate. Uponanalysis it was found that 56% of'the oil originally dissolved in theortho-nitroanisole was solubilized and extracted by the tri-amylamine.

The residual fraction, 1. e. the ortho-nitroanisole and its dissolvedoil, was then subjected to vacuum distillation to recover the solvent.It was found, similarly, that a slight amount of the tri-amylamine wascontained in the ortho-nitroanisole condensate. The extract remainingafter the distillation and removal of the selective solvent was a highlyviscous, tacky, tarry mass.

Under the conditions of the treatment, therefore, the original oil wasfractionated into a typical rafiinate, a second clarified fraction, 1.e. the extract from the tri-amylamine phase, and a highly viscousresidue. The rafiinate constituted approximately 71% of the originalcharge; the

clarified tri-amylamine extract substantially 16% of the originalcharge, while but approximately 12% was recovered in the viscousresidue.

The effectiveness of the treatment in separating the constituents of theoriginal oil is seen from a comparison of the tri-amylamine extract andthe ortho-nitroanisole extract. The original oil had a viscosity of 265Saybolt seconds at 100 F. and 46.6 Saybolt seconds at 210 F. Thetri-amylamine extract had a viscosity of 555 Saybolt seconds at 100 F.and 55.3 Saybolt seconds at 210 F., and a viscosity index of 9. Theheavy residuum, on the other hand, had a viscosity of 115 Sayboltseconds at 210 F.

It is to be observed that the clarified naphthenic fraction, ortri-amylamine extract, although of a low viscosity index, isnevertheless a commercially useful fraction and employable,

for example, -asa medium quality light lubricant.

The essential features of the improved method of "fractional separationof oil therefore comprises, extracting agiven mixed base oil fractionwith-a solvent which has -a preferential affinity forthe non-paraffinicbodies, then further treating the solvent phase with a clarifying oilsolvent, at any temperature at which the two solvents will not form ahomogeneous liquid phase so --a's to establish stratification of therespective solvents and their dissolved constituents. The secondextraction, as will be appreciated may be carried out at any'temperaturebelow the miscibility temperature of the two solvents chosen. Otherthings being equal, the higher the miscibility temperature of the twosolvents and the greater the selectivity of the selective solvent,

the greater willbe the permissive thermal operative range and thegreater will be the corresponding permissivevariation of thecharacteristics of the clarified extract. Again, as will be understood,the lower the solubility of a solvent of given selectivity, the greaterwill be the quantity of oil extracted by the clarifying solvent.

The choice of the selective and clarifying solvents, as is understood bythose skilled in the art,will'be determined by a number of factors, suchas: the character'of the stock to be treated, the quantity of andcharacteristics desired in the ultimate fractions, the type of plantequipment available, and the like.

The process is, of course, operable with a relatively wide rangeofselective solvents, that is to say, t*he-invention is-by no meanslimited to the use of-the highly selective solvents enumerated. Thus,for the selective solvent utilized for the preliminary extraction theremay be employed, in addition to ortho-nitroanisole andorthomethoxybenzonitrile, other solvents of marked selectivity, such asfurfural, aniline and the like. As explained, the particular clarifyingsolvent which ischosens'houldbe correlated with the selectivesolventfand upon the basis of-the factors given the optimum clarifyingsolvent for any given operation can readily be determined.

With highly selective solvents, such as orthonitroanisole, th quality ofrafiinate that may be produced, when utilizing a given oil-solventratio, depends essentially on the oil outlet temperature of the system.Similarly, the yield or quantity of the raffinate depends essentially onthe solvent outlet temperature. The characteristics of the secondfraction, for any given clarifying solvent and operating conditions,will thus be governed to a considerable degree by th extractionconditions obtaining in the first refining stage.

When refining a Mid-Continent oil, for example, by solvent extractionwith selective solvents, a relatively large sacrifice in yield must bemade inorder to secur a small increase in viscosity index when theviscosity index of the raflinate is about 90. Generally when a singleselective solvent is employed for the fractionation, it is not usuallyeconomical to make too great a sacrifice in yield in order to obtain thehighest viscosity index oil. The operations conducted heretofore have,therefore, necessarily been a compromise between these factors. It willreadily be appreciated that under the present method, assuring as itdoes the production of a second Valuable product, this sacrifice inyield can more readily be made, thus insuring recovery of the optimumquality of lubricating stock, coupled with the maximum recovery ofvaluable oil fractions.

It is to be understood that the operations described herein need not becarried out under conditions controlled to insure a substantiallyquantitative separation of the parafiinic constituents in the firstextraction stage. If the selective solvent extract does contain someamount of parafl'inic oil, upon the addition of the second solvent whichis immiscible with the selective solvent, the residual paraifinicconstituent will largely be taken up in the second solvent because ofthe greater afiinity of the selective solvent for the naphthenicconstituents. In other words, the second solvent displaces the remainingparaffinic constituents from the selective solvent phase.

The principles of the invention may be effected by a number ofspecifically different methods and by utilizing different types ofapparatus. In a typical commercial embodiment, for example, a given oilfraction may be contacted with the selective solvent, such asorthonitroanisole, in a suitable batch or continuous countercurrentsystem, as more particularly explained in application Serial No. 60,634.If a light oil is to' be refined, the first extraction step may beoperated with an oil outlet temperature in the approximate range of fromabout 115 C. to 120 C. more or less. The solvent outlet temperature maybe maintained at approximately 60 C. These temperatures, as is known,will be controlled depending upon the quality and yield of raflinatedesired. After stratification and separation of the raffinate in anysuitable manner, the solvent phase may, if desired, be cooled further toinsure the separation of an additional quantity of the raffinate.

The cold solvent phase may then be contacted with a suitable secondsolvent, such as tri-amylamine, in a second batch or countercurrentsystem. In this manner the immiscible second solvent extracts from theselective solvent-oil phase a considerable fraction of the dissolvedoil. The temperature at which the second extraction is efiected may becontrolled at any degree below the miscibility temperature of theselective solvent and the clarifying solvent. The yield and quality ofoil removed in the clarifying solvent phase can therefore be controlledwithin relatively wide ranges.

The viscous, residual fraction produced in the system may be utilized asa cracking stock. Since this stock contains a relatively high percentageof the heavy hydrocarbons, cracking may be carried out at relatively lowtemperatures. This fraction may also be suitably processed as by steamdistillation, air blowing and the like, to produce valuable, marketableasphaltic products.

While th improved method of treating petroleum oil has been described asbeing particularly applicable to the refining of lubricating oilfractions, it is to be understood that it is not limited to thisparticular stock. The principles of the invention may be invoked in anycircumstances where it is desired to secure the selective recovery ofsimilar petroleum oil constituents from any initial mixtures thereof.Hence, while preferred modifications of the invention have beendescribed, it is to be understood that these are given to illustrate theprinciples involved and not as defining the exclusive methods ofeffectuating these principles.

We claim:

A process of refining petroleum hydrocarbons which comprises, contactinga mixed base petroleum oil with furfural at a temperature above themiscibility temperature of the oil and the solvent; stratifying the massinto an oil phase and a solvent phase; separating the solvent phase withits dissolved naphthenic constituents from the oil phase; cooling thesolventphase to remove additional quantities of oil therefrom, and thentreating the solvent phase, at relatively low temperatures, withtriamylamine which is characterized by a substantial immiscibility withfurfural at said temperature.

ARTHUR W. HIXSON. RALPH MILLER.

